Atherosclerosis is the leading cause of morbidity and mortality in the US. In this grant, we will examine the role of metabolite sensitive receptors on muscle afferent neurons in the responses of sympathetic nerve activity after limiting blood flow to hindlimb muscle, as seen in peripheral arterial occlusive disease due to atherosclerosis. A rat model of femoral artery occlusion will be used to restrict hindlimb blood flow. The specific aim 1 is to examine expression of transient receptor potential vanilloid type 1 (TRPV1), purinergic P2X receptors, and acid sensing ion channels (ASICs) and responsiveness to activation of those receptors. Based on our published work and pilot data collected for this proposal, we hypothesize that femoral artery occlusion augments the reflex sympathetic response due to increases in those receptors' expression and responsiveness in dorsal root ganglion (DRG) neurons innervating muscles. The specific aim 2 is to examine the role of nerve growth factor (NGF) in responses of TRPV1, P2X and ASICs. We hypothesize that NGF in the DRG neurons is a key factor for development of abnormality in reflex sympathetic response after artery occlusion. Our pilot data have shown that levels of NGF are increased in DRG neurons of rats with artery occlusion. We anticipate that NGF infused in the muscle of healthy rats using an osmotic minipump will induce an increase in sympathetic response to activation of those receptors or muscle contraction; and neutralization of NGF will improve the reflex sympathetic response in rats with femoral artery occlusion. The specific aim 3 is to examine the role of by-products in responses of TRPV1, P2X and ASICs. We hypothesize that accumulated metabolites in the muscle have an important contribution to abnormal sympathetic response after femoral artery occlusion. We anticipate that artery occlusion will elevate muscle by-products such as ATP, acid, etc. to a greater degree as compared with control. We further anticipate that chronic infusion of by-products in the muscle of healthy rats will augment the reflex responses as seen in rats with arterial occlusion via respective receptors. Finally, we anticipate that attenuating those receptors will improve the sympathetic responses.